Author ORCID Identifier

https://orcid.org/0000-0003-1891-1278

Year of Publication

2020

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Agriculture, Food and Environment

Department

Animal and Food Sciences

First Advisor

Dr. Paul Priyesh Vijayakumar

Second Advisor

Dr. Melissa Morgan

Abstract

Fresh produce is one of the most common sources of food-borne outbreaks, involving various pathogenic microorganisms such as Escherichia coli. Recent outbreaks have clearly shown that post-harvest washing has limited effectiveness on decontaminating produce and may contribute to cross-contamination of produce due to various limitations. Excessive use of sanitizers and antibiotics has also led to the development of many antibiotic-resistant strains of bacteria that have made the food industry more vulnerable.

Bacteriophages are a bacterial viruses that can selectively infect and replicate within bacteria leading to cell lyse and death. Bacteriophages have become widely recognized due to their ability to selectively eliminate bacteria. Furthermore, their effectiveness in infecting and successfully eradicating various multi-drug resistant strains of bacteria has shown promise in a time of antibiotic resistance. It is for these reasons that bacteriophages are being proposed as an alternative to antibiotics for treating infections in humans, animal production, and as a biocontrol in food for bio-preservation and safety.

Four bacteriophages (C14s, V9, L1, and LL15) of bovine origin were used against E. coli O157:H7 to study their efficacy against the pathogen under a controlled and complex environment. A microplate study was used to demonstrate this effectiveness under numerous conditions. A significant reduction (P< 0.01) in the pathogen was observed. The subsequent study challenged the phage cocktail with 100-ppm bleach and 100-ppm SaniDate 5.0 respectively for three hours to study the ability of phages to tolerate the commercially used sanitizers. The bacteriophages survived the sanitizer concentration and significantly reduced (P< 0.05) the population of the pathogen. A temperature study was conducted to analyze the ability of bacteriophage to withstand varying temperatures as a component of produce washes with mild heat treatments. Bacteriophages were subjected to 35, 45, and 55°C and were spot tested for effectiveness. The results indicated their ability to tolerate an increase in temperature and effectively produce plaques compared to the control.

The success in demonstrating the phage's ability to reduce pathogens in a controlled environment led to the development of challenging them in a more complex environment, namely a produce wash. Fresh spinach leaves were washed with E. coli O157:H7 and bacteriophage cocktail in organic-rich and sterile water. The results indicated that there was a significant reduction (P< 0.01)in the pathogen under both conditions. The successive study tested the same conditions in the presence of both sanitizers (100-ppm) and bacteriophage cocktail in sterile and high organic load produce wash. The sanitizer made in sterile wash water significantly (P< 0.01) reduced the pathogen in the presence or absence of a bacteriophage cocktail. However, in the presence of an organic load, the data demonstrated that compared to the control, the phage cocktail significantly reduced (P< 0.01) the contamination of the pathogen on the spinach leaves. These results demonstrate the ability of bacteriophages to be used in a produce wash system during post-harvest sanitation to act as a biocontrol in reducing pathogen contamination on fresh produce.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.081

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